Control inverter change-over system



M. K1" PARKHuRsT CONTROL INVERTE CHANGE-OVER SYSTEM Nov. 5, 1946.

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Patented Nov. 5, 1946 UNITED .STATI-:s PATE Azyilolus NT oFFlcE f CONTROL INVERTER CHANGE-OVER SYSTEM MalcolmA K. Parklxurst. New York', N. Y., assignor. to The Wilcolator Company,vElixabeth, N. J., a corporation of Delaware L Application Augustz'l, 1945, Serial No. 611.783

(Cl. ITI-97) that certain heavy aircraft are equipped with a main inverter and a spare inverter for producing alternating current for electrical circuits used in the control of superchargers and other equipment aboard the aircraft, such circuits employing 115 volt,'400 cycle alternating current. The inverter usedto produce this current is a motor generator set comprising a direct current motor coupled to a 115 volt alternating current generator. g

The application referred todiscloses an auto. matic change-over relay system for immediately initiating the operation of the spare inverter upon the failure of the main inverter. This system, ac-

l cording to the'application, includes an alternating current relay with a normally closedand normally open contact, a direct current relay with the combination of a normally open and a normally closed contact, and a separate normally closed and anormaily open contact, a time-delay relay, means for supplying direct current through the D. C. relay for starting the main inverter, means for Supplying direct cur-rent to the timedelay relay. means for supplying alternating current from the main inverter as soon as it is in operation, to energize the A. C. relay and thereby form a normally closed contact, means for energizing the D. C. relay from the time-delay relay, and means for passing direct current through the energized D. C. relay for immediately initiating the operation of the spare inverter when 4the A. C. relay is de-energized upon the failure of the main inverter.- I'he application discloses other features. such as the use of a heater-oper ated time-delay relay, and means for maintain-` ing the D. C. relay energized independent of the time-delay relay, and for de-energlzing the heater-operated relay upon initially energizing the D. C. relay. y Certain problems have arisen in connection with the operation of very heavy aircraft such as four-motor bombers. and other heavy aircraft, because of the momentary heavy loads placed upon the main inverter and the batteries carried 2 by such aircraft. It has been found, for example, that the initial heavylload employed on opening bomb-bay doors causes such a current drain on the main inverter that the spare inverter has been cut into th system. It has also been found that in certain instances, a heavy drain on the battery has Islowed the main inverter to such an extent as to cause the change-over relay to cut in the spare inverter. 'Ihe importance of such occurrences can be readily/appreciated when it is understood that the pilot or the flight engineer will believe from the showing of his instruments that the main inverter has failed. This may lead to a change of plans or the interruption of aflight mission as well as other complications readily apparent to those familiar with the operation of very heavy aircraft. ,se

The primary object of the present invention is therefore tolprovide an automatically-controlled inverter change-over system which willsolve the problem and avoid the cutting in of the spare 'inverter when in fact the main inverter has not failed or been put out of action. i

A furthe object of the invention is to provide a system such as that referred to in which a momentary failure of the main inverter or its slowing down momentarily, is insumcient to operate the relay system to cut in the spare inverter.

According to the present invention, the automatic control change-over relay system includes a time-delay relay, an A. C. relay, and a D. C. relay, as in the case of the system disclosed in the abovementioned application, but these relays are interconnected by distinctly dierent circuits to accomplish the features and objects of the present invention. The various relays are connected in such a way that when the pilot closes his main switch to start the main inverter, it, and not the spare inverter is energized. Furthermore, the

circuits connecting the various relays of the system are arranged so that a momentary interruption, or drain on the main inverter or on the D. C. current, does not cut in the spare inverter, but sets up a circuit which would eventually cut in the spare inverter if an interruption .or drain continues beyond a predetermined time.

An important feature of the present invention is the provision of a circuit which, upon the closing of the pilot switch, establishes a substantially direct line for the starting of the main inverter and closes a circuit to the time-delay relay. The connections tothe output of the main inverter, however, are such that prior to the operation of the time-delay relay at this stage, the A. C. relay opens. switch in the circuit to the time-delay r relay. thereby preventing the cutting in of the spare inverter.

Another important feature of the present invention is the provision of means whereby the A. C. relay keeps the switch open to the timedelay relay. However, the arrangement is such that this switch may close, upon a momentary failure of A. C. current or when the current partially fades out. The time-delay relay is then started, but it is set so that it will not cut in the spare inverter in a period of less than two seconds. The arrangement is such that a revival of the main inverter, in a period of no more than five seconds, opens the switch to the time-delay relay and prevents the cutting in of the spare inverter.

Another important feature of the present invention is the arrangement of a circuit for cutting in the spare inverter upon the failure of the A. C. current for a predetermined time and the resulting de-energizing of the A C. relay. The occurrences of 'these events energize the time-delay relay which in turn energizes the D. C. relay which operates a switch to cut in lthe spare inverter and to cut out the heater or operator of the time-delay relay.

Other features, objects and advantages of the present invention will be described in greater detail in the following description in conjunction with the accompanying drawing illustrating one form of the improved automa-tic change-over system.

In the drawing, the single figure is a schematic wiring diagram showingI the preferred arrangement of the variouselements of the system and circuit, and its association with the circuits of the main and spare inverters used for supplying alternating current.

Referring to the drawing, the improved automatically controlled inverter change-over system and circuit is shown in conjunction with D. C. power relays for initiating the operation of main and spare inverters. as also shown in the pending application. The control system per se is illustrated primarily in a rectangular enclosure I centrally located in the figure of the drawing. D. C. current, as for example, from batteries, is

supplied to the apparatus through a feeder bar I2.

As in the application referred to above, the apparatus illustrated includes a main inverter or motor generator I4, a D. C. power relay Il oi' conventional design for the main inverter I4, a spare inverter Il, a D. C. relay like the relay Il, for the ilspare inverter, an inverter-failureindicating signal 22, and a relay 23 therefor.

Direct current for operating the inverters I4 and Il, as well as the alternating current generated by the inverters, are supplied through the separate relays Il and 20 which are operated from the automatic system included in the closure IIl. The D. C. current, for example, such as 29 volts current, is supplied from batteries or other sources through the feeder bar I2 and leads 24, through the relays Ii and 20, to the inverters I4 and Il. I'he 115 volt, 400 cycle alternating current generated bythe inverters I4 and Il is conducted through feeder lines 24, and 29 volt D. C. or 115 volt A. C. current may be conducted through parallel feeder lines 20. The three switches in each of the D. C. power relays Ii and 2l remain open until they are closed when these relays are energized to supply D. C. current to either of the inverters I4 or Il through line 24, and deliver .the generated alternating current into the main A. C. feeder lines 2O and 24.

According to the present invention, D. C. current is supplied from the feeder bar I2 to the change-over relay system through a lead 30 provided with a main or pilot switch 32 which is connected to a terminal 34 of the change-over unit shown in the enclosure I0. The various leads, such as 24 and 30, from the D. C. feeder bar I2, are provided with fuses 35. The closing of the pilot switch 32 establishes a 29 volt D. C. circuit from the feeder bar I2 through the terminal 34, a line 3B, a normally closed switch I8, comprising a, part of a D. C. relay 40, a line 42, a terminal 44 and a line 46, connecting into the coils of the D. C. power relay I6. The coils of the relay I6 are grounded as indicated. and the flowv of current through the line 46 closes the three switches in the relay and therefore supplies 29 volt D. C. current through the line 24, through this relay, to the inverter I4 which is immediately put in operation.

D. C. current supplied through the terminal 34 also passes through a line 48y an initially closed switch .50 of an A. C. relay 52, a line 54 which leads to a thermostatic bimetal contact switch arm 58 comprising a part of a heater-operated time-delay relay 58. The line 54 has a branch line leading through an initially closed switch 82, operated by the D. C. relay 4U. The switch l2 is initially closed with a line 84 connected into a heating element 68 of the heater-operated timedelay relay 68. The outlet of the heating element 86 leads to a ground line 68 and a terminal 10 which is connected to ground as shown.

As soon as the inverter I4 is placed in operation and alternating current builds up in the line 2i, this current is conducted through a connecting line 12, through a terminal 14 in the enclosure I0. and a line 18 to the coil of the A. C. relay I4. which is connected to the ground line B8. 'Ihe energizing of the relay B2 occurs immediately upon the-production oi' A. C. current in the system, and Itherefore opens the switch .50 and cuts 01T the D. C. current initially flowing to the timedelay relay 58 through the lines 54 and 80, before the closing of the time-delay relay switch.

The continuous flow of alternating 'current from the main inverter I4 through the lines 12 and 1B and the relay 52, maintains the switch ll open, otherwise the switch is biased to a closed position and is therefore set for closure upon the failure. or reduction, of the A. C. current supplied to the relay 52. The interruption of the flow of current through the relay 52 permits the switch l0 to close and thereby effect a circuit through the heater of the relay 58 which begins the hea-ting of the bimetal of the switch Il. If the interruption of current to the relay l2 is only a momentary matter, this relay will be re-energized and reopen the switch lll prior to the closing of the switch 58. Under these conditions, therefore, there would be no change from the main inverter to the spare inverter.

The nature of these momentary interruptions and reductions in the flow of 'A. C. current have been explained above. Under certain circumstances, however, the main inverter I4 may actually fail or be knocked out by enemy action, and when this happens, the switch l0 closes and supplies current to the relay 5l to close the switch 5B. The instant the switch 5I closes, two things happen: (1) A circuit is established through a line 18, a line I0 leading to a terminal I2, and a line I4, to the coils of the D. C. power relay 2l, which starts the operation of the spare inverter I8 lto supply A. C. current. I2) At the same time andere the line 18 and a connecting line 88, through the coil oi' the relay 40, which is grounded to the ground line 68.

When the relay 40 is energized in this manner, the switch 621s opened, thereby cutting the current to the heater B6, and the lever of switch IB is swung to de-energize relay I8 and to connect with a line 88, which in turn connects into the lines 86 and 80 to provide for the direct supply of D. C. current from the terminal 34 to the relays 20 and 40. After the spare inverter rent relay having a normally open switch and two normally closed switches, .a time-delay heater-operated relay for closing a switch which is normally open, a source of direct current for said relay system, means for establishing a ldirect current circuit through one of the closed switches of said D. C. relay to means for starting the .main inverter. for generating alternating cur- Il has been cut into the system in the manner described, and the relay I8 de-energized, no alternating current is passing .through the relay l2. The switch 50 remains closed to supply current through the switch $6 to the relay 0 until the relay cools and the switch 58 open opening of the switch 58 will merely cut on the ow of current through the line M to thel relays 20 and 40, but these relays are' now sup- *plied with current directly from the terminal through the switch 3B and line 88.

The time-delay relay 58 is arranged so that the heating is sufficiently slow to prevent the closing ofthe switch in a period of less than 2 seconds, and in any event it must close in no more than 5 seconds. This will allow for any temporary interruption in the alternating current from the main inverter without causing a change-over from the main to the spare inverter.

The heater relay is also preferably constructed so that it vwill cool rapidly after being de-ener` gized, so that the plane can be tested quickly. If the main inverter Il is inoperative or out-ofcommission at the time oi' the closing of the pilot switch 22, the relay B2 will not be energized, but the time-delay relay il will be energized to cut in the spare inverter i8 and operate the relay 40 to establish permanent'circuits to the relays and 40, and to cut out 'the heater or other operator of the time-delay `ure in the supply of A. C. current. D. C. is conducted to this relay from the feeder bar I2 through aline 90 while a lead 02 connects into the A. C. line 20. The relay 23 is grounded, as indicated, and connected by a line M to the signal 22 which is also grounded. Whenthe alternating current in the` line 28 is interrupted, the relay 2l is de-energied to cut ofi'the supply of direct current to the signal 22.

The relays i6 and 2li are standard D. C. power relays, and certain of the elements within the enclosure lll are also standard. Different relays may be employed than those indicated within the enclosure Ill, so long as they are adapted present invention. The heater-operated timedelay relay or switch is merely one example or a time-delay relay which might be used to establish the circuits as described at the prescribed periods oiI time in the cycle of operations. Various other modifications may be made in the apparatus without departing from the spirit and scopeof the present invention, as defined by the claims.

What I claim is:

1. An automatically controlled inverter changeover relay system for supplying alternating current from a spare inverter following the failure of a main inverter for producing alternating current, comprising an alternating current relay having an initially closed switch, a direct cur- Thev rent, means for simultaneously establishing a direct current circuit through the heater of the time-delay relay, means for establishing an alternating current circuit from the current output of the main. inverter through the alternating current relay for opening the switch associated therewith, means whereby said heateroperated relay establishes a circuit for energizing the D. C. relay-to open said closed switches and close the normally open switch to establish a circuit from the direct current source to means for starting the spare inverter, the energizing of said D. C. relay also opening the circuit through the heater of the time-delay relay.

2. An automatic electrical 2relay`unit for supplying alternating current from a 7spare inverter following the failure, of a main inverter for producing alternating current, comprising/'an alternating current relay and a switch openedthereby, a D. Cr relay having a normally open switch and two normallyclosed switches, a time- `circuit throughv one of the closed switches of said DL C. relay to means for startingV the main inverter, means for simultaneously initiatfing theestablishment of a direct current cirv to carry out the functions and objects ofthe cuit through the time-delay relay, means for establishing an alternating current circuit from the current output of the main inverter through the alternating current relay for opening the switch associated therewith, means whereby said time-delay relay is adapted to establish a circuit for energizing the D. C. relay to open said closed switches an'd close the normally open switch to establish a circuit from the direct current source to means for starting the spare inverter and to establish a circuit for keeping the D. C. relay energized.

3.V An automatic electrical relay unit for supplying alternating current from a spare inverter following the failure of a main inverter for producing alternating current, comprising an alternating current relay and a switch opened thereby, a- D. C. relay having a normally open switch and two normally closed switches, a time-delay relay having a switch which is norm'ally open, a source of direct current for said relay unit, means for establishing a direct current circuit through one of the closed switches of said D. C. relay to means for starting the main inverter, means for simultaneously initiating the establishment of a direct current circuit through the time-delay relay, means for establishing an alternating current circuit from the current output of the main inverter through the alternating current relay for opening the switch associated therewith, means including the time-delay relay operative after a predetermined time following the failure of the main inverter for starting the spare inverter and for establishing a circuit for energizing the D. C. relay to thereby open said closed switches and close the normally open switch to thereby establish a circuit from the direct current source to the means for starting the spare inverter and to 7 establish a circuit for keeping the D. C. relay energized.

4. In an automatic inverter change-over system for supplying current from a spare inverter following the failure of a main inverter normally used i'or supplying such current, a relay, a heatresponsive switch provided with an electric heater ,operable by current flow therethrough to cause erate said heat-responsive switch and initiate the operation o! the spare inverter after a predetermined time.

5. In an automatic inverter change-over system for supplying current from a spare inverter following the failure of a main inverter normally used for supplying such current, a relay, a timedelay switch operable by current flow thereto to cause the closing of said switch after the passage of current thereto for a predetermined period of time, means for starting the spare inverter and for energizing said relay upon the closing of said switch, said relay being adapted to establish a circuit for the operation of the spare inverter, a circuit including a switch for supplying current to said time-delay switch, means responsive to the current generated by said main inverter i'or opening the switch in said last-mentioned circuit, said last-mentioned switch being biased to a closed position whereby the failure of the main inverter causessaid last-mentioned switch to close thereby supplying current to `said time-delay switch to cause it to close and start the operation of the spare inverter.

6. In an automatic change-over system for supplying current from a spare current source upon the failure of current normally supplied from a main current source, a relay, a current-operated time-delay switch operable by the iiowof current thereto to cause the closing o! said switch after thc passage oi' current thereto for a predetermined period of time, circuit means for energizing said relay and for initiating the supply of current from said spare current source upon the closing of said switch, said relay being adapted to establish a circuit for the supply of current from said spare current source, a circuit including a switch for supplying current to said time-delay switch, and means responsive to the tlow of current from said main current source for opening the switch in said last-mentioned circuit, said last-mentioned switch being normally biased to a closed position whereby the failure of current supplied from said main current source permits said last-mentioned switch to close to in turn permit current to flow therethrough to said time-delay switch MALCOLM K. PARKHURST. 

